Motor control system



Dec. 26, 1933. C; w. wYMAN 1,940,926

MOTOR CONTROL SYSTEM Filed May* 28, 1930 "M1-Mm. v

Patented i Dec. 26, 1933 UNITED STATES MOTOR CONTROL SYSTEM Charles W. Wyman, Claremont, N. H., assigner to Sullivan Machinery Company, a corporation of Massachusetts Application May 28, 1930. Serial No. 456,761

14 Claims. (Cl. 175r294) This invention relates to motor control systems and mechanisms, and more particularly to improved means for maintaining an alternating current motor circuit closed notwithstanding the occurrence of relatively low voltages.

The holding in of direct motor circuit controlling contactors upon occurrence of relatively low voltages does not present the difficulties which are present when alternating currents are used, due to the fact that direct current control permits the solenoid relays or other devices in use to hold in over very extended drops in voltage, whereas in alternating currents the drop in voltage which may occur before the control elements drop out is much smaller.

It is an object of my invention to provide improved means for holding in an alternating current motor notwithstanding a drop in voltage substantially below that which would normally permit the same to drop out. A further object is to provide improved mechanism whereby this operation is effected automatically. A still further object is to provide improved means whereby the contactor solenoid or coil resistance is varied automatically as the voltage drops. A still further object in this respect is to vary, if desired, the resistance of the contactor coil itself, although it is to be understood that resistance may be associated with the contactor coil and appropriately controlled to effect the desired results, it being understood that in any case the variation ofthe. resistance, whether of the coil itself or of outside resistance, is such that the necessary holding force of the contactor coil would be maintained irrespective of very low voltages. Other objects have to do with improved means whereby variations of this resistance are effected without unnecessary arcing during operation of the switches, and the provision of improved circuits associated with the low voltage arrangements.

Other objects and advantages will be readily understood by those skilled in the art from the following description and the accompanying drawing:

In this drawing,

Fig. 1 is a wiring diagram illustrating diagrammaticallythe various elements and circuits of an illustrative embodiment of my improved arrangement. v

Fig. 2 is a fragmental view of a modified system in the main similar to that of Fig. 1.

1n the illustrative embodiment (shown in Fig. l) of my invention alternating current is supplied from main linesv L1, Lz and La through a manually operated main switch 1 and thence through a triple pole contactor generally indicated at 2, to a motor 3. A suitable reversing switch 4 may be provided and in addition the mainline leads may include the coils of an overload relay 5, or other relay coils for any desired purpose. Herein the overload relay 5 is provided preferably with a delay dash pot 6.

The contactor 2 is operated by a solenoid 7, and upon the existence of a sufficient voltage, this solenoid is energized by current owing from line Lz through wires 8, 9, pilot switch 10, contacts 11 closed by switch bar 12, wire 13, contacts 14 closed by a contact bar 15, wires 16 and 17, to the main line La. A solenoid 18 is provided for controlling the position of the contact bar 15 in accordance with main line voltage variations, and is energized by currentv supply through wires 19, 20 and 2l disposed in parallel with the wires 8 and 17. If the voltage drops below a predetermined value, the solenoid 18 permits its contactor bar l5 to drop, but a circuit for maintaining the main contactor 2 closed is maintained due to the provision of contacts 22 which are so disposedrelative to the other contacts 14 that the contactor bar 15 bridges both the contacts 14 and22 when passing from one to the other. Of course, the contact bar 15 finally leaves the contacts 14 when it is fully engaged with the contacts 22. This arrangement not only minimizes arcing, as contact bar 15 passes from one set of contacts to the other,y

but also still supplies current to a portion of the coil 7 by way of wire 23, contactor interlock switch 24, and wire 25 which is vconnected to an intermediate portion of the contactor coil 7. Solenoid 18 is designed to permit lowering ci bar 15 to close the circuit between contacts 22, before the voltage drops sufficiently to cause solenoid 7 to permit the contactor 2 to open.

It should be noted that in the particular embodiment of the invention disclosed in Fig. 1, the resistance oiered by the portion of the contactor coil above the lead 25 is substantially less than one half the total resistance of the entire contactor coil 7. Accordingly, the reduction in the number of turns is more than compensated forv by an'increase in the current which flows through the active portion of the coil 7, with a result that a lower voltage applied to the heavier, still active portion of the coil 7 will maintain the line contactor 2 closed, than would maintain the contactor closed when the whole coil 7 is ,energized. By way of illustration let it be assumed that were the switch 15 held inits upper position and current flowing through the wire 16 to the entire coil 7, the contactor would be maintained closed until the voltage dropped to .6 of the normal full line voltage. Now, if the coil 7 be so constructed that the number of turns at each side of the connection 25 is the same but that .7 of the resistance of the coil is in the lower half thereof, it will be evident that when the bar 15 is connecting the contacts 22, the line voltage may drop to somewhat less than .4 of its full value before the line contacter 2 will be opened. It will, of course, be understood that the construction oi' the coil 7 or the use of resistance in conjunction with it will depend upon the minimum voltage to be permitted. Preferably part of the resistance of the contactor coil als cut out when the voltage drops to about of normal. vIt will be observed that notwithstanding the presence of this automatic control means, the contactor will inherently open automatically due to insuiiicient holding current in the active part oi coil 7 when the voltage drops to some predetermined minimum value below which it is not desired to maintain the contactor closed. When the contactor does open, its interlock switch also opens thereby necessitating the restoring of voltage to a relatively high value, perhaps of the full line voltage, before the low voltage relay 18 will pull its contact bar 15 into engagement with the contacts 14 and thus reestablish current -flow to the main line contactor solenoids 7.

It is thus seen that the main line contacter is kept closed after the voltage falls to a value which would cause the contactor to open were the present invention not employed, and also during the existence of even a further drop in voltage, but that upon the occurrence of a predetermined minimum voltage, the contactar opens; also that after the contactor opens, it cannot be reclosed until reestablishment of a relatively high voltage.

In case of overload, switch 12 is moved upwardly by overload energlzation of coils 5, thereby closing contacts 27 to energize holding coil 28 as by current owing through Wires 29, 21 and 17 to the other main line. 'I'his operation breaks the current flow through contacter coil 7 and thus opens the main line switch. To reestablish current ow through the solenoid it is first necessary to manually open the pilot switch 10 and thus break the circuit through holding coil 28 whereby contacts 11 are'again closed and ii' the overload condition no longer prevails and the voltage is at a proper value, contactor coil 7 will be energized again to close the main line switch 2. The-dash pot 6 will retard opening of contacts 1l for a sumcient brief interval oi time thereby permitting any momentary excess load from breaking current supply for motor 3.

In Fig. 2 an illustrative embodiment somewhat difl'erent from that in Fig. 1 is disclosed. Instead of making the solenoid 7 as in the modiilcation of Fig. 1 and cutting out some of the turns and thereby a greater percentage of the resistance inherent in the coil, the resistance is structurally separate from the solenoid and is in series with the solenoid when the relay switch 15 is in its upper position and is cut out when the relay switch 15 assumes its lower position. In

this illustrative embodiment it will be noted that a resistance R is connected between the lower end oi.' the main line switch operating solenoid 7' and the lett hand contact 14 by means of the conductor 18', and that the conductor 25 leads to the lower end and not to an intermediate point in the solenoid 7. 'I'he system is otherwise' the same as shown in Pig. 1.

'I'he mode o! operation o! this modified system does not require extended description. It will be evident, however, that when the manually operable switch 10 is closed, a circuit will be effected through the wire 13, right hand contact 14, switch bar 15, lett hand contact 14, conductor 16', resistance R. and the coil 7', and that themain line switch 2 will be closed. When this is closed, the interlock 24 will close the circuit between the conductors 23 and 25 and upon voltage drop sufficient to allow the switch bar 15 to move to a position connecting the contacts 22, the current will be supplied directly to the solenoid 7 and not through the resistance 16. Accordingly, though there will be no increase in turns in the solenoid, there will be an increase in the current which passes through the solenoid, and by appropriately regulating the relative resistances of the resistance R and the solenoid 7', the main line switch may be caused to hold in until the line voltage drops of! to a very low fraction, the operating characteristics being much the same as that of the mechanism of Fig. l. As the operation of the system will be clear with this description, detailed analysis is unnecessary.

In both forms of the invention it will be evident that upon a drop in line voltage suilicient to permit switch 1`5 to move from contacts 14 to contacts 22, there will be a change in the actuating circuit which controls the main line switch so that the magnetomotive force applied in holding the main line switch closed will be greater in proportion to the voltage applied to the actuating circuit than is the case when the line voltage is near normal. In the case of each illustrative system, the value of the ratio between the effective number of turns operating to hold the main line switch closed and the resistance of the circuit of which the turns form a part will be increased when the relay moves fromits upper to its lower position. Y

It is thus seen that I have provided improved arrangements whereby the main line ontactor is maintained closed through a wider range of voltage drop than is ordinarily the case with alternating current and that this operation is eil'ected automatically and in conjunction with suitable safety circuits such as the overload relay. It is also necessary for the voltage to drop through two successive low limits before the con-y tactor is thrown out and once the contacter is opened it is necessary for reestablishment of a i assume in practice, it will be understood thatl these forms of the same are shown for purposes of illustration, and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope ot the appended claims.

What I claim as new and desire to secure by Letters Patent is: f

1. In a motor control system, in combination, a source of A. C. power supply, a motor, a line switch for connecting the motor to the source of power, and an actuating circuit for the line switch having, irrespective of the voltage variations in said power supply, a voltage between its ends which bears continuously the same ratio to the voltage of the power supply, said actuating circuit including force applied at said switch and the voltage applied to said circuits.

3. In a motor control system, A. C. power lines, a motor, a main line contactor for connecting said motor to said lines, and operating and controlling means for said contactor including a circuit having a magnetic coil and oi' a predetermined resistance, and means operative on a predetermined drop in line voltage automatically to increase the value of the ratio between the effective number of turns in said coil and the resistance of said circuit.

4. In a motor control system, A. C. power lines, a motor, a main line contactor for connecting said motor to said lines, and operating and controlling means for said contactor including a circuit containing a solenoid comprising two portions, the ratio of its respective number of turns to its resistance being greater in one of said portions than in the other, and means operative on a predetermined drop in line voltage automatically to eliminate from said circuit the portion in which said ratio is the lower.

5. The combination with a source of supply and an electric motor, of a control system for the motor comprising a contactor disposed to connect the motor to the source of supply, a relay disposed to be responsive to iluctuations of the supply voltage, a two part operating magnet for saidcontactor, circuits respectively including both parts and but a single part of said magnet, the magnetomotive force of said entire magnet for a given applied voltage being less than that of said single part for the same applied voltage, said relay movable to establish the iirst named one oi said circuits when the line voltage is relatively high and to establish the other on a. predetermined drop in line voltage, and an interlock associated with said second circuit and movable with said contactor to closed position on closing of said contactor.

6. The combination with a source o! supply and an electric motor, of a control system for the motor comprising a contactor disposed to connect the motor to the source of supply, a relay disposed to be responsive to iluctuations or the sunply voltage, a two part operating magnet for said contactor, circuits respectively including both parts and but a single part of said magnet, said relay movable to establish the tlrst named one of said circuits when the line voltage is relativehr high and to establish the other on a predetermined drop in line voltage, an interlock associated with said second circuit and movable with said contactor to closed position on closing of said contactor, and an overload relay controlling both of said circuits.

'1. In a motor control system, in combination, power lines, a motor, a switch for connecting the motor to the power lines, electromagnetic operating means for said switch deriving its operating E. M. F. at all times exclusively and directly from said power lines, aline voltage responsive device, and means controlled thereby for variably connecting saidv electromagnetic operating means with the power lines to vary the ratio between the electra-motive force exerted and the line voltage.

8. In a motor control system, in combination, a source of power supply, a motor, a line switch for connecting the motor to the source o! power supply and disconnecting it therefrom, an muating circuit for the line switch having a portion including an actuating solenoid for the line switch, said portion of said actuating circuit supplied with current whose potential bears a substantially constant ratio to the potential of said source of power supply, and means for varying the resistance of said portion of said actuating circuit automatically upon a predetermined drop in voltage at the line switch.

9. In a motor control system, in combination, a urce of power supply, a motor, a line switch for connecting the motor to the source of power, circuits for electromagnetically actuating and holding said line switch, a line voltage responsive relay, and means controlled thereby for increasing the ratio between the magnetomotive force applied at said switch and the voltage applied to said circuits.

10. In a motor control system, power lines, a motor, a main line contactor for connecting said motor to said lines, and operating and controlling means for said contactor including a circuit having a magnetic coil and of a predetermined resistance, and means operative on a predetermined drop in line voltage automatically to increase the value of the ratio between the effective number ofy turns in said coil and the resistance of said circuit. l

11. In a motor control system, power lines, a motor, a main line contactor for connecting said motor to said lines, and operating and controlling means for said contactor including a circuit containing a solenoid comprising two portions, the ratio of its respective number of turns to its resistance being greater in one of said portions than in the other, and means operative on a predetermined drop in line voltage automatically to eliminate from said circuit the portion in which said ratio is the lower.

12. In a motor control system, in combination, a source of A. C. power supply, a motor, a line switch for connecting the motor to the source of power, an actuating circuit for the line switch, and means for decreasing the resistance of said actuating circuit automatically upon predetermined drop in voltage at the line switch.

13. In a motor control system,.in combination, a source of power supply, a motor, a line switch for connecting the motor to the source of power, an actuating circuit for the line switch, and means for decreasing the resistance of said actuating circuit automatically upon predetermined drop in voltage at the line switch.

14. In a motor control system, in combination, a source of A. C. power supply, a motor, a line switch for connecting the motor to the source of power, actuating means for the line switch including a coil including a plurality oi.' turns, branching connections leading from one end or said coil and respectively of different resistances, a switch device, conductors leading respectively to the other end o! said coil and to said switch device and supplied with current whose potential varies directly with the A. C. power source, said switch device movable to connect said last mentionei'l conductor selectively to one or the other of said branched connections, and means for moving said switch device automatically on a predetermined drop in voltage at the line switch to vary said connections and thereby vary the resistance of said actuating circuit.

CHARLFBW.WYMAN. 

